Meteors, meteoroids, and meteorites are different terms that can often be confused, but shouldn't be. Rocks or dust floating freely in space are meteoroids. A meteor is a shooting star in the sky—it's a space rock burning up in our atmosphere. If a piece of this material makes it all the way through the atmosphere and hits the ground, we call it a meteorite.
Have you ever seen a shooting star? If you've been out stargazing, you've probably noticed what looks like a star streak across the sky, then disappear. Shooting stars, or falling stars, are technically called meteors. Most are small grains of dust, or occasionally tiny pebbles, and are often leftover debris from comets. These are, in fact, the smallest particles that orbit the Sun. Shooting stars might appear blue and white, or perhaps yellow and orange—the color can depend on the speed at which the meteor is traveling.
FIGURE 8-3:An artistic rendering of a meteor storm(refer to page 279 for more information)
Why do they look so bright? These tiny pebbles are little pieces of space junk that occasionally crash into Earth's atmosphere, but since they're so small, they usually don't make it to the ground. They enter the atmosphere at such high speeds that bits of gas trapped in the rock are vaporized, producing a very bright glow—the bright streaks we call shooting stars. Meteors are visible to us on Earth only when they pass into Earth's atmosphere.
Generally, one or two meteors will be visible on just about any night you're out looking at the stars. A few times a year, though, meteor showers occur. The most famous is the Perseids, which is visible every year around August 11 and 12. When Earth passes through part of its orbit that contains more dust and small rocks than usual, we see meteor showers.
Since we go around the Sun once a year, we pass through this dirty area once a year, predictably about the same time each year. Why is this particular area of space so dirty? Blame a comet! The reason it's dirty is because Earth crosses through the trail of debris left by a comet as it neared the Sun. The gas and dust blown off a comet as it partially disintegrates leaves a trail behind it, even after the comet itself is long gone.